2,2{40 -bis(3-pyridinols)

ABSTRACT

The novel compounds, 2,2&#39;&#39;-bis(3-pyridinols), will fluoresce in the visible spectrum when exposed to ultraviolet light. The particular color emitted is dependent upon the other substituents on the pyridine ring. Generally, the parent compound and its substituted derivatives fluoresce green, unless the substituents have aromatic or aliphatic unsaturation which is conjugated with the unsaturation of the pyridine ring. This shifts the fluorescence to longer wavelengths, so that it is possible to produce compounds which fluoresce in the yellow and red portions of the visible spectrum. The compounds are readily soluble in common organic solvents and are thermally stable. They can be incorporated in various polymers to impart their fluorescent properties to the polymers. They can be incorporated in lacquers to produce films or applied as coatings on the envelope of ultraviolet lamps to produce various colored lights when energized.

United States Patent Wirth July 11, 1972 [54] 2,2-BIS(3-PYRIDINOLS)Joseph G. Wirth, Schenectady, N.Y.

[73] Assignee: General Electric Company [22] Filed: Jan. 7, 1970 [21]Appl. No.: 1,318

[72] Inventor:

Otroshchenko et al., Chemical Abstracts, Vol. 63,4248- bd,( 1965)Primary Examiner-Alan L. Rotman Attorney-Richard R. Brainard, Joseph T.Cohen, Paul A. Frank, Charles T. Watts, James W. Underwood, Frank L.Neuhauser, Oscar B. Waddell and Joseph B. Forman ABSTRACT The novelcompounds, 2,2 '-bis(3-pyridinols), will fluoresce in the visiblespectrum when exposed to ultraviolet light. The particular color emittedis dependent upon the other substituents on the pyridine ring.Generally, the parent compound and its substituted derivatives fluorescegreen, unless the substituents have aromatic or aliphatic unsaturationwhich is conjugated with the unsaturation of the pyridine ring. Thisshifts the fluorescence to longer wavelengths, so that it is possible toproduce compounds which fluoresce in the yellow and red portions of thevisible spectrum. The compounds are readily soluble in common organicsolvents and are thermally stable. They can be incorporated in variouspolymers to impart their fluorescent properties to the polymers. Theycan be incorporated in lacquers to produce films or applied as coatingson the envelope of ultraviolet lamps to produce various colored lightswhen energized.

5 Claims, No Drawings 1 2,2'-BIS(3-PYRIDINOLS) This invention relates to2,2-bis(3-pyridinols), also known as 2,2-bis(3-hydroxypyridines). Morespecifically, this invention relates to the chemical compounds havingthe fonnula 5 N R1- z where R, R R and R are independently selected fromthe group consisting of hydrogen, halogen, lower alkoxy, lower alkyl,phenyl substituted lower alkyl, lower alkenyl and phenyl substitutedlower alkenyl. When exposed to a source of ultraviolet light, thesecompounds fluoresce emitting light in the visible region. The particularcolor which they emit depends on the R substituents.

Although there are many known organic compounds which have fluorescentproperties, generally the visible light which they emit is so weak thatthey can not be incorporated in minor amounts into other compositions toimpart fluorescent properties thereto. Only very few organic compoundshave strongly fluorescent properties so that they can be used in suchapplications. However, these materials generally are photochemically,oxidatively or thermally unstable at relatively low elevatedtemperatures so that upon long term exposure to ultraviolet light, airand especially at elevated temperatures, they lose their fluorescentproperties.

For most applications, requiring long term stability of the fluorescentproperties, inorganic phosphors have been used. Unlike organicmaterials, which depend upon their chemical structure for thefluorescent properties, inorganic materials depend upon a particularcrystal structure for their fluorescent properties. This means that theycan not be used in solution and also when incorporated as a solid intoother compositions, care must be taken not to destroy the crystalstructure responsible for the fluorescent property. For example, whenincorporating such inorganic phosphors as pigments in a paint or othercoating composition, great care must be taken not to shear or grind thepigment, thereby, destroying its crystal structure, during theoperations necessary to disperse the pigment in the paint or coatingcomposition.

As a powder, or dispersed pigment, one particle overlaying anotherparticle will shield the latter from the exciting light. This means thatthere is a practical limitation, both on the concentration of thedispersed pigment in the coating composition as well as on the thicknessof the coating composition which is deposited on an object if it isdesired to excite from one side of the layer, for example, aself-supporting film or a coating on a transparent substrate and havethe light emitted from the fluorescent pigment visible on the otherside.

I have now discovered that the bis-pyridinols having the above formulacan be prepared by oxidative coupling of the corresponding pyridinolusing lead dioxide as the oxidizing agent. Other oxidizing agents can beused, but are not as effective as lead dioxide. These bis-pyridinols arestrongly fluorescent when irradiated with ultraviolet light. Thecompounds are readily soluble in common organic solvents and even verydilute solutions (less than 1 percent by weight) fluoresce strongly. Theintensity of fluorescense is apparently invariant with the excitingwavelength of light in the range of from about 1,800 to 4,000 A., butthereafter decreases, appreaching zero at approximately 5,200 A. Thecompounds are 70 oxidatively and thermally stable and melt withoutdecomposition. Therefore, they can be readily incorporated into apolymeric matrix, preferably one which is essentially colorless, byeither solution or melt processing techniques. Only a very small amount,1 percent by weight or less, is required to 75 impart the stronglyfluorescent color properties to the objects fabricated from thepolymeric composition.

The particular color which is emitted by these compounds when excited byultraviolet light is dependent upon the particular R substituent. Whenthe R substituents are hydrogen the compound fluoresces blue-green. Whenthe R substituents are halogen, alkoxy, alkyl or aralkyl the compoundsall fluoresce with the same brilliant green color within the limits ofdetection. Since, the length of the alkyl chain in the R group has noefiect on the emitted color, there is no incentive for having any alkylsubstituent, either per se, or as part of the other substituents, e.g.,alkoxy, aralkyl, etc., be anything but lower alkyl, i.e., having fromone to eight carbon atoms, for example, methyl, ethyl, propyl,isopropyl, butyl (including the various butyl isomers), the variouspentyl isomers, the various hexyl isomers (including cyclohexyl), thevarious heptyl isomers and the various octyl isomers. When the Rsubstituents have aromatic or aliphatic unsaturation, preferably aphenyl ring or an olefinic group, which is conjugated with theunsaturation of the pyridine ring, i.e., there is unsaturation betweenat least the alpha and beta carbon atoms of the substituent, thespectrum of the emitted light is shifted to the longer wavelengths. Aphenyl substituted olefinic group where the unsaturation of the phenylgroup is conjugated with the unsaturation of the olefinic group, whichin turn is conjugated with the unsaturation of the pyridine ring, willcause a greater shift than the same olefinic group without the phenylsubstituent.

If the unsaturation of the substituent is not conjugated with theunsaturation in the pyridine ring, little if any noticeable shift in thewavelength of the emitted light over that of the unsubstituted,halo-substituted, or alkyl-substituted pyridine is noted. Therefore,when aliphatic unsaturation is present in the substituent, it preferablyis between the alpha and beta carbon atom of the substituent withrespect to the attachment to the pyridine ring if only a singleunsaturated bond is present i.e., it has a, B-unsaturation. If multiplealiphatic unsaturated bonds are present in the substituent theypreferably are conjugated with each other and one of them is between thealpha and beta carbon atom. Olefinic unsaturation is at least aseffective as acetylenic unsaturation in causing the shift in emmission.Since olefinically unsaturated substituents and especially a, B-olefinically unsaturated substituents are more easily introduced on thepyridine ring, they are preferable to the corresponding acetylenicsubstituents. Although any aryl substituent can be used to providearomatic unsaturation, aryl groups other than phenyl are not any moreeffective, are more difiicult to introduce into the pyridine compoundsand decrease the oxidative and thermal stability of the resultingcompounds. Therefore, I prefer to use phenyl as the aryl substituentwhen aromatic unsaturation is desired. If the phenyl group is directlyattached to the pyridine ring, the unsaturation of the phenyl group isconjugated with the unsaturation of the pyridine ring. However, it wouldbe extremely difficult to produce the requisite phenyl substitutedpyridinol or bipyridinol. It is much easier to have the phenyl group asa substituent on any olefinic group in which the olefinic unsaturationis already conjugated with the unsaturation of the pyridine ring.Introduction of electron donating groups as substituents on the phenylgroup causes a still slightly further shift than is accomplished by thephenyl group itself. Unfortunately, such electron donating groups, forexample, amino and mono and dialkyl substituted amino groups decreasethe oxidation resistance of the compounds and their presence duringtheir coupling reaction can cause some side reactions. Such substituentscan be present on the phenyl group if the loss of oxidative stabilitycan be tolerated but if present, preferably are introduced after thecoupling reaction.

From what is said above, it is apparent that the conjugation of theunsaturation is desirable since it ,is a means of shifting thewavelength of the emitted light. However, where such shift is notdesired, the unsaturation does not need to be conjugated with theunsaturation of the pyridine ring. Like the alkyl groups discussedabove, the alkenyl groups preferably are lower alkenyl, examples ofwhich are vinyl, allyl, 1,2-propenyl, the various butenyl isomers, thevarious butadienyl isomers, the various pentenyl isomers, thepentadienyl isomers up to and including the various octenyl isomers, theoctadienyl isomers, octytrienyl isomers, etc. The phenyl substitutedalkyl and phenyl substituted alkenyl may be any of the above alkyl andalkenyl groups having one or more phenyl groups substituted thereon,typical examples of which are: benzyl, aand B-phenylethyl, aandB-styryl, ,Bfi-diphenylethenyl, 6-phenyll,3,5-hexatrienyl, etc.

Insofar as I can determine, the number of substituents of any oneparticular kind on the bis(3-pyridinols) has little if any effect on theshifting of the spectrum of the emitted light, for example, when allfour Rs are methyl, the emitted light is essentially the same greencolor as obtained when only two of the R groups are methyl and the othertwo hydrogens and there is only a slight shift to a longer wavelength inthe red region caused by an additional phenyl group in theB-diphenylethenyl group compared to the B-styryl (B-phenylethenyl)group.

Oxidative coupling of an equimolar mixture of two different3-pyridinols, will produce a mixture of three 2,2-bis( 3- pyridinols)which can be separated. Two of the products will be the symmetricalcompounds that would have been obtained if each of the 3-pyridinols hadbeen coupled in separate reactions with the third product being theunsymmetrical product containing a pyridinol ring of each of thestarting materials. This latter compound when irradiated withultraviolet light will emit a color intermediate between the two colorsproduced by the symmetrical compounds. Although I have produced suchcompounds, basically there is no incentive towards doing this since thecolor I obtained is the same color that I can obtain by mechanicallymixing or dissolving equimolar amounts of the two symmetrical compoundsin a mutual solvent. By varying the proportions of the two compounds, Ican obtain mixtures whose fluorescent colors cover the complete spectrumintermediate between the two emission colors of the compounds in themixture.

Apparently the fluorescent properties of the bis( 3- pyridinols) arerelated to hydrogen bonding occurring between the hydroxyl group in onepyridine ring with the nitrogen on the other pyridine ring. For example,if an ethanol solution of one of the bis(3-pyridinols) is titrated withalcoholic sodium hydroxide while being irradiated with ultravioletlight, the color emitted shifts gradually to shorter wavelengths untilthe monosalt is formed. As the titration is continued the intensity ofthe fluorescence decreases until sufficient alkali is added to form thedi-salt at which point the fluorescense completely disappears.

Apparently, the mono-salt can only exist in solution, since onevaporation of the solution containing only a sufficient amount ofsodium hydroxide to produce the mono-salt, the disalt will precipitateleaving the balance of the bis( 3-pyridinol) in the hydroxide form. Thisis easily followed under ultraviolet light since the di-salt will becompletely colorless and the wavelength of the emitted color will shiftback from the shorter wavelength of the mono salt in solution to thelonger wavelength of the bis(3-pyridinol). Redissolving the mixture ofthe di-salt and the free bis( 3-pyridinol) in solvent, will again formthe color of the mono-salt. Unusual color effects can be obtained onchromatographic plates or even filter paper by first applying a spot ofthe solution of the mono salt and then rewetting the spot after thesolvent evaporates and chromatographic separation of the mixturesoccurs. Under ultraviolet irradiation, the colors change, disappear andreappear as the solvent evaporates and is replenished and as the di-saltgets separated from and changes the ratio present in the free bis(3-pyridinol) thereby changing the ratio of the latter to mono-salt onrewetting and dissolution. If the initial bis( B-pyridinol) fluorescesin the red region the more spectacular the various colors produced willbe with the shift to the shorter wavelengths since the shifting occursthrough a wider portion of the visible spectrum.

In order that those skilled in the art can readily understand myinvention, the following examples are given by way of illustration andnot by way of limitation. In all of the examples, parts and percentagesare by weight and temperatures are in degrees Centigrade. Whereelemental analyses are given, the calculated values are given inparentheses following the determined values. The wavelengths reportedare those where the emission spectrum of a methylene chloride solutionof the compound shows a maximum.

The method of E. Koenigs, H.C. Gerdes and A. Sirot, Ben, 61, 1022 (1928)was used to prepare 6-chloro-3-pyridinol. The method of R. Adams and TR.Govindachari, J. Am. Chem. Soc., 69, 1806 (1947), was used to prepare6-methoxy- 3-pyridinol. The method of E. Plazek, Ben, 72, 577 (1939) wasused to prepare 4,6-dimethyl-3-pyridinol. Both 3- pyridinol and6-methyl-3-pyridinol are commercially available. Lithiation of thelatter compound by standard techniques lithiates the methyl group, ahighly colored product which can be titrated with reactive halides orcarbonyl compounds. This procedure was used to prepare the various highalkyl, phenylsubstituted alkyl and phenyl-substituted alkenyl compoundsof the examples. The general procedure for preparing these derivativesis as follows:

A solution of 6-methyl-3-pyridinol in anhydrous tetrahydrofuran iscooled to 0 C., treated with two equivalents of n-butyllithium in hexanesolution and stirred for approximately 1 hour to give a suspension ofthe deep red lithiated intermediate. Addition of one equivalent of analkyl halide (methyl iodide, ethyl bromide, propyl bromide, benzylchloride etc.) causes immediate discharge of the red color and thereaction mixture is then poured into water. Neutralization of theaqueous phase followed by extraction of the product with ether gives the6-alkyl-3-pyridinol or 6-(phenylalkyl)-3- pyridinols.

Addition of one equivalent of an aldehyde or ketone (benzaldehyde,benzophenone, acetone etc.) to the lithiated pyridinol suspension causesimmediate discharge of the red color and formation of an intermediatealcohol. Reaction with acetic anhydride gives a diacetate which ontreatment with sodium bicarbonate undergoes an elimination reaction toform a 6-alkenyl-3-acetoxypyridine. Finally, hydrolysis with 20 percentaqueous sodium hydroxide gives the 6-alkenyl-3- pyridinol or6-(phenylalkenyl)-3-pyridinol.

The general procedure for oxidative coupling of the various 3-pyridinolsto their corresponding 2,2-bis(3-pyridinols) was as follows:

A solution of the 3-pyridinol in benzene in which lead dioxide wassuspended, was heated at reflux with stirring for a period of 12 hours.After filtering off the lead residue, various techniques were used toisolate the desired 2,2-bis(3- pyridinols), as given in the specificexamples.

EXAMPLE 1 A solution of 0.95 g. of 3-pyridinol in ml. of hot benzenecontaining 1.20 g. of lead dioxide was reacted as described in thegeneral procedure. After a short time, an intractable tarry materialbegan to coat the lead dioxide causing it to deposit on the sides of thereaction vessel and interfering with the reaction. Thin layer and vaporphase chromatographs showed that the benzene soluble portion contained alarge amount of the starting material and a small amount of compoundhaving a brilliant blue-green fluorescense (4,800 A.) when exposed toultraviolet light. Extraction of the tarry residue with hot benzene gaveadditional amounts of the two materials. The vpe retention time and thebrilliant fluorescense indicated that the product was 2,2'-bis(3-pyridinol).

This product was synthesized by an independent method whereincommercially available 2-iodo-3-pyridinol in tetrahydrofuran at 0 C.,was reacted with two equivalents of n-butyllithium followed by additionof one equivalent of copper trifluoroacetate and air oxidation for 10minutes. The reaction mixture was poured into water, the aqueous phaseseparated and then acidified to pH 6. Extraction with ether andevaporation of the extract to dryness gave the desired2,2'-bis(3-pyridino1) in a 27 percent yield along with a small amount ofunreacted 2-iodo-3-pyridinol, which was separated from the desiredproduct by preparative thin layer chromatography. This product likewisehad a brilliant blue-green fluorescence, and had an identical vaporphase chromatography retention time and identical mass and infraredspectra with the product obtained by the lead dioxide oxidation process.

A portion of this product purified by recrystallization from ethanolfollowed by sublimation had a melting point of 188 190 and analyzed: C,63.5 (63.8); H, 4.6 (4.3); N, 14.5 (14.9).

EXAMPLE 2 A solution of 1.09 g. of 6-methyl-3-pyridinol in 100 ml. ofhot benzene was oxidatively coupled with 2.38 g. of lead dioxide usingthe general procedure. Thin layer and vapor phase chromatographs showeda single product containing unreacted starting material. Filtration andevaporation of the filtrate to dryness gave a residue weighing 0.85 g.,which upon extraction with percent petroleum ether gave a pale green,brilliantly fluorescent solid (5,050 A.). It was recrystallized frompetroleum ether to give 0.23 g. of material having a molecular weight,determined by osmometry of :10 (216). The nmr and mass spectra and acomparison of infrared spectra with the same compound synthesizedindependently in low yield by heating a mixture of commerciallyavailable 2-iodo-6-methyl-3-pyridinol with copper powder and sublimingthe product as formed showed that the product was 2,2-bis(6-methyl-3-pyridinol). After recrystallization from petroleum ether, theproduct had a melting point of 189 190 and analyzed: C, 66.8 (66.7); H,5.6 (5.6); N, 13.0 (13.0).

EXAMPLE 3 and mass spectra also indicated that the product was 2,2-

bis(6-ethyl-3-pyridinol). Confirmation of the structure was obtained byreaction of the product of Example 2 with four equivalents ofn-butyllithium followed by reaction with methyl iodide to give a producthaving the same mass and infrared spectra. After recrystallization fromether/ petroleum ether, the product had a melting point of 117 119 andanalyzed: C, 69.0 (68.8); H, 6.6 (6.6): N, 11.4 (11.5).

EXAMPLE 4 A solution of 0.137 g. of 6-n-propyl-3-pyridinol. in 25 ml. ofbenzene was oxidatively coupled with 0.239 g. of lead dioxide using thegeneral procedure. After filtration and solvent removal, extraction ofthe residue with 20 percent ether 30 60 petroleum ether gave 0.047 g. ofa pale green, brilliantly fluorescent crystalline solid (5,050 A.) whichwas further purified by recrystallization. Again, the IR spectrum showedstrong hydrogen bonding of the hydroxyl group. The nmr and mass spectraindicated that the product was 2,2'-bis( 6propyl- 3-pyridinol). This wasconfirmed by independent synthesis from the product of Example 2 bylithiation and reaction with ethyl bromide. The recrystallized producthad a melting point of 91 C., and analyzed: C, 70.7 (70.6); H, 7.4(7.4); N, 10.2 (10.3).

When this example was repeated but using an equivalent amount of6-n-butyl-3-pyridinol in place of the 6-n-propyl-3- pyridinol, theproduct was identified as 2,2'-bis-(6-butyl-3- pyridinol).

EXAlVIPLE 5 A solution ofO. 199 g. of 6-( 2-phenylethyl)-3-pyridinol in20 ml. of benzene was oxidatively coupled with 0.239 g. of lead dioxideby heating for 8 hours at reflux. After filtration of the reactionmixture to remove the lead oxide, the residue obtained by evaporation ofthe solvent was redissolved in ether 30 60 petroleum ether andcrystallized by cooling in a solid carbon dioxide-acetone bath to give0.061 g. of a pale yellow solid which under ultraviolet light had astrong green fluorescence (5,050 A.). Infrared, nmr and mass spectrashowed the compound to be 2,2'-bis[6-(2-phenylethy1)-3- pyridinol]. Thesame product was also obtained by lithiating the product of Example 2and reaction with benzyl chloride. After recrystallization fromethanol-water, the product had a melting point of 151 52 and analyzed:C, 78.7 (78.8); H, 6.2 (6.1); N, 6.9 (7.1).

EXAMPLE 6 A solution of 0.129 g. of 6-chloro-3-pyridinol in 20 ml. ofbenzene was oxidatively coupled with 0.238 g. of lead dioxide by thegeneral procedure. Filtration and evaporation of the filtrate to drynessgave 0.036 g. of a residue which on treatment with a limited quantity ofmethylene dichloride dissolved the desired product from the unreactedstarting material. After evaporating the solvent and sublimation, 0.016g. of a solid was obtained which under ultraviolet light had a palegreen brilliant fluorescense (5050A.). It had a melting point of 228230, and was shown by nmr and mass spectra to be the desired 2,2-bis(6-chloro-3-pyridinol).

EXAMPLE 7 A solution of 0. 13 g. of 4,6-dirnethyl-3-pyridinol in 20 ml.of benzene was oxidatively coupled with 0.239 g. of lead dioxide usingthe general procedure. The product was isolated from the filtrate byevaporation of the solvent and extraction of the residue with hot 30 60petroleum ether as a solid which under ultraviolet light had a palegreen, brilliant fluorescence (5,050 A. Sublimation under reducedpressure gave 0.029 g. of an essentially pure product, which was shownby infrared, nmr and mass spectra to be 2,2'-bis-(4,6-dimethyl-3-pyridinol). After repeated recrystallizations from hexaneether, theproduct had a melting point of 238 240 and analyzed: C, 68.9 (68.8); H,6.7 (6.6); N, 11.3 (11.5).

EXAMPLE 8 A solution ofO. g. of 6-methoxy-3-pyridinol in 20 ml. ofbenzene was oxidatively coupled with 0.239 g. of lead dioxide bystirring at room temperature for 12 hours. Thin layer and vapor phasechromatography showed a small amount of unreacted starting material andtwo major products, only one of which had hydroxyl groups. The desiredproduct was separated by filtration of the benzene solution followed byextraction with 5 portions of 2N sodium hydroxide. Neutralization of thebase extract with dilute sulfuric acid, extraction with ether, drying ofthe ether extract over sodium sulfate and evaporation to dryness gave0.05 g. of a solid which under ultraviolet light had a pale green,brilliant fluorescence (5,050 A.). The nmr and mass spectra showed thatthe compound was 2,2-bis( 6-methoxy-3-pyridinol). Afterrecrystallization and sublimation, the product had a melting point of191 193 and analyzed: C, 58.2 (58.1); H, 4.9 (4.9); N, 11.2 l 1.3

EXAMPLE 9 When equimolar amounts of 6-methyl-3-pyridinol and 6-ethyl-3-pyridinol were cooxidized by the general procedure, 3

EXAMPLE 10 A solution of 6.7 g. of 6-(2-styryl)-3-pyridinol, also called6- (2-phenylethenyl)-3-pyridinol, in 300 ml. of benzene was oxidativelycoupled with 16.2 g. of lead dioxide using the general procedure, butrefluxed for 20 hours. After filtration, the filtrate on evaporationgave a tarry residue from which the product was isolated by preparativethin layer chromatography. Recrystallization from glyme, the dimethylether of ethylene glycol, gave red needles having brilliant red-orangefluorescence under ultraviolet light (5,750 A.). The melting point was230. The uv and ir spectral characteristics were consistent with theexpected product 2,2-bis-[6-(2-styryl)-3- pyridinol] which can also benamed 2,2-bis-[6-(2-phenylethenyl)-3-pyridinol]. Confirmation of thecompound was obtained by hydrogenation of the product which converted itto a pale green solid having brilliant green fluorescence (5,050 A.)under uv light and which was shown to be identical with the productproduced in Example 5 by vapor phase chromatography retention time andinfrared spectra.

EXAMPLE 1 l A solution of 1.49 g. of 6-isobutenyl-3-pyridinol in 100 ml.of benzene was stirred 12 hours at room temperature with 2.39 g. of leaddioxide. After filtration and solvent removal the dark-colored residuewas distilled to give an orange crystalline product which had abrilliant yellow fluorescence (5,500 A.). Recrystallization from ethergave 0.46 g. of pure material which was shown to be2,2'-bis(6-isobutenyl-3-pyridinol) by ir, nmr and mass spectra.

EXAMPLE 12 A solution of 0.253 g. of 6-(2,2-diphenylethenyl)-3-pyridinol in ml. of benzene was heated under reflux with 0.44 g. of leaddioxide for 90 hours. After filtration and solvent removal the reactionmixture was separated by preparative thin layer chromatography to give0.044 g. of pure material. The product was an orange-red solid with abrilliant orange-red fluorescence (5,800 A.). Its identity as2,2'-bis[6- (2-diphenylethenyl)-3-pyridinol] was established from uv, irand mass spectra.

EXAMPLE 13 A benzene solution containing equimolar amounts of 6-methyl-3-pyridinol and 6-(2-phenylethenyl)-3-pyridinol was heated underreflux with lead dioxide for hours. The products were isolated bypreparative vapor phase chromatography. Two of them were identical withthe symmetrical dimers obtained in Examples 5 and 10. The remainingproduct was an orange solid with a brilliant yellow fluorescence (5,500A. Its identity as the mixed dimer 6-(2-phenylethenyl)-6'-methyl-2,2-bis( 3-pyridinol) was established from ir, nmr and massspectra.

EXAMPLE l4 Fluorescent lacquers were obtained by dissolvingpolymethylmethacrylate and a small amount (0.1-3 percent based on theweight of polymer) of one or more 2,2-bis(3- pyridinols) in methylenechloride, the color of the fluorescence being determined by substituentson the pyridine nucleus as discussed above.

Gas discharge lamps emitting light of wavelengths which readily passthrough the glass envelope of the lamps and excite the fluorescence ofthe 2,2-bis( 3-pyridinols) were coated by dipping in the lacquers andair drying for 1-2 hours. When energized the lamps produced light whichwas the color produced by the fluorescence of the particular 2,2-bis-(3- pyridinol) in the coating on the envelope.

The above examples have illustrated many of the variations andmodifications of the invention. Many other wide and useful applications,in addition to those already disclosed may be made of the compositionsof this invention, especially when incorporated in various resincompositions. Obviously, other modifications and variations of thepresent invention are possible in light of the above teachings. It istherefore to be understood that changes may be made in the particularembodiments of the invention described which are within the fullintended scope of the invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates Patent Office is:

1. Chemical compounds having the formula,

where R, R, R and R are independently selected from the group consistingof hydrogen, halogen, lower alkoxy, lower alkyl, and lower alkenyl.

2. The compounds of claim 1 wherein R, R, R and R are lower alkyl.

3. The compounds of claim 1 wherein R and R are lower alkyl and R and R"are hydrogen.

4. The compound of claim 1 wherein R and R are methyl and R and R arehydrogen.

5. The compound of claim 1 wherein R and R are l-isobutenyl and R and Rare hydrogen.

2. The compounds of claim 1 wherein R1, R2, R3 and R4 are lower alkyl.3. The compounds of claim 1 wherein R1 and R2 are lower alkyl and R3 andR4 are hydrogen.
 4. The compound of claim 1 wherein R1 and R2 are methyland R3 and R4 are hydrogen.
 5. The compound of claim 1 wherein R1 and R2are 1-isobutenyl and R3 and R4 are hydrogen.